Low-temperature-resistant, halogen-free, flame retardant polyolefin-based resin composition

ABSTRACT

A halogen-free flame-retardant polyolefin resin composition which can give a molded article improved in low-temperature resistance and surface whitening resistance and improved in flame retardancy and melt index, and an expansion-molded article having uniform and fine gas bubbles without large-sized gas bubbles, the halogen-free flame-retardant polyolefin-based resin composition containing a polyolefin resin, a dihydric or trihydric metal hydroxide surface-treated with a saturated fatty acid, or, when the metal hydroxide is aluminum hydroxide, aluminum hydroxide surface-treated with a saturated or specific unsaturated fatty acid or an alkali metal salt thereof, and an aluminum salt of an unsaturated fatty acid having 10 to 30 carbon atoms.

BACKGROUND OF THE DISCLOSURE

1. Field of the Invention

The present invention relates to a halogen-free flame-retardantpolyolefin-based resin composition improved in low-temperatureresistance (cold weather resistance). More specifically, it relates to ahalogen-free flame-retardant polyolefin-based resin composition which isfree from a surface whitening phenomenon and which is improved in flameretardancy and melt index and is also improved in low-temperatureresistance. Further, the present invention relates to anexpansion-molded article of the above resin free of large-sized gasbubbles.

2. Description Art of Related

Polyolefin resins are easily combustible themselves. It is thereforenecessary to impart polyolefin resins with flame retardancy forpreventing various calamities caused by fire, etc., and a variety ofproposals have been hitherto made. One proposal is concerned with aflame-retardant polyolefin-based resin composition obtained byincorporating an organic halide or a combination of an organic halideand antimony trioxide into a polyolefin resin.

However, the problem of the above resin composition is that it corrodesa molding machine when molded. Further, it generates a large volume ofsmoke in fire, and the smoke is toxic and corrosive. For overcomingthese problems, there has been proposed a method in which aflame-retardant polyolefin-based resin composition is provided byincorporating a large amount of a halogen-free safe flame-retardant suchas magnesium hydroxide or aluminum hydroxide into a polyolefin resin.This method is disclosed in many publications such as JP-A-50-119848,JP-A-53-12943, JP-A-54-77658, JP-B-57-10898, JP-A-60-243155 and U.S.Pat. No. 4,396,730

A polyolefin-based resin composition obtained by incorporating a largeamount of metal hydroxide into a polyolefin resin satisfies thepractical use level requirements of mechanical strength at roomtemperature (ordinary temperature), and causes almost no problem whenused in a warm environment. However, this polyolefin-based resincomposition has a problem on low-temperature resistance since it shows agreat decrease in mechanical strength, particularly impact strength,when used at a low temperature. That is, the polyolefin-based resincomposition has a problem in that it is embrittled in a low-temperatureenvironment so that the use thereof in such an environment isunacceptable or impossible.

The term "low-temperature resistance" in the present specificationspecifically means the following. A resin composition having"low-temperature resistance" refers to a resin composition which showsalmost no decrease in impact resistance such as Izod impact strength anddu Pont impact strength when used at a low temperature such as atemperature below the freezing point, or which shows a sufficiently lowbrittle temperature in a brittle temperature test. A material having nolow-temperature resistance is embrittled and unsuitable as a materialfor use in a low-temperature environment such as a cold district or anextremely cold district.

However, the above publications on flame-retardant polyolefin-basedresin compositions do not recognize anything concerning the need forimprovement in low-temperature resistance, and naturally, thosepublications describe nothing concerning low-temperature resistance. Theproperties of a polyolefin-based resin composition differ depending uponwhether or not a metal hydroxide incorporated as a flame retardant issurface treated. The metal hydroxide which is not surface-treated haspoor compatibility with a polyolefin resin so that it cannot behomogeneously dispersed in the resin. As a result, a mixture of theseshows a low melt index, and a molded article of the mixture(composition) is very poor in toughness low-temperature resistance andflame retardancy. Further, when the metal hydroxide is other thanaluminum hydroxide, a composition of these shows a high surfacewhitening phenomenon.

On the other hand, a surface-treated metal hydroxide not only hasexcellent compatibility with a polyolefin resin but also has excellentdispersibility in polyolefin resin. Therefore, a mixture of asurface-treated metal hydroxide and a polyolefin resin has a greatlyimproved melt index, and a molded article thereof has excellenttoughness at room temperature. Further, the surface whitening phenomenonof a molded article of a mixture containing a surface-treated metalhydroxide other than aluminum hydroxide and a polyolefin resin isconsiderably inhibited when some surface-treating agents are selected.However, the low-temperature resistance and flame retardancy of thesecompositions is still at low levels.

Further, the expansion molding method has a problem in that large-sizedgas bubbles occur so that it is difficult to obtain an expansion-moldedarticle having uniform and fine gas bubbles.

JP-A-50-119848 discloses a self-distinguishing resin composition whichis improved in melt index for easy injection molding, by incorporating,as a lubricant, a salt of a fatty acid having 8 to 20 carbon atoms and ametal such as aluminum, zinc, magnesium or calcium into aself-distinguishing polyolefin-based resin composition containingmagnesium hydroxide. However, JP-A-50-119848 mentions nothing concerningthe surface treatment of the magnesium hydroxide, and does it describeanything concerning the low-temperature resistance of theself-distinguishing resin composition as an end product. Theself-distinguishing resin composition actually has a very low level oflow-temperature resistance, and its flame retardancy is also poor.

JP-A-53-12943 discloses that a polyolefin-based flame-retardant resincomposition of which the flame retardancy, toughness and injectionmoldability are well-balanced and excellent can be obtained byincorporating metal soap as a lubricant and an alkali metal salt of anorganic carboxylic acid as a flame retardant aid into a flame-retardantpolyolefin-based resin composition containing magnesium hydroxide.However, JP-A-53-12943 does not mention anything concerning the surfacetreatment of the magnesium hydroxide, nor does it describe anythingconcerning the low-temperature resistance and the surface whiteningphenomenon of the polyolefin-based flame-retardant resin composition.This resin composition actually has the following problems. It has poorlow-temperature resistance, the surface whitening phenomenon isintensified by adding an alkali metal salt of an organic carboxylicacid, and a molded article obtained therefrom is degraded in appearance.JP-A-53-12943 uses Izod impact strength values according to ASTM D-256for toughness evaluation. ASTM D-256 is a method in which Izod impactstrength is measured at a temperature of 23° C. ±2°C. A flame-retardantpolyolefin-based resin composition according to JP-A-53-12943 shows ahigh Izod impact strength value at room temperature, while it shows avery low one at a temperature below the freezing point. Further, thealkali metal salt of an organic carboxylic acid does not show the flameretardant aid effect as much as that described in JP-A-53-13943. Themelt tension of the flame-retardant polyolefin-based resin compositionis very low. As a result, strands thereof easily break when processedwith a resin processing machine such as an extruder, and it is verydifficult to continuously process it with a pelletizer.

U.S. Pat. No. 4,396,730 discloses a flame-retardant thermoplastic resincomposition containing magnesium hydroxide surface-treated with analkali metal salt of oleic acid as a flame retardant and a magnesiumoleate or aluminum oleate as a flame retardant aid. U.S. Pat. No.4,396,730 seeks to provide a resin composition which has excellentmoldability and gives a molded article having improved flame retardancy,an excellent appearance and excellent strength. However, it pays noattention to the surface whitening phenomenon. That is, the surfacewhitening phenomenon cannot be avoided when an alkali metal salt ofoleic acid is used, and the alkali metal salt of oleic acid isnevertheless used for surface-treatment of magnesium hydroxide. For thisreason, the resin composition of U.S. Pat. No. 4,396,730 has a defect inthat a molded article therefrom suffers a surface whitening phenomenonto a great extent. Further, U.S. Pat. No. 4,396,730 describes nothingconcerning the low-temperature resistance of the resin composition.

JP-A-54-77658 discloses a resin composition obtained by incorporatingpolyvinyl acetate or an ethylene-vinyl acetate copolymer as a flameretardant aid into a flame-retardant olefin polymer containing magnesiumhydroxide. However, JP-A-54-77658 describes nothing concerning thelow-temperature resistance. The resin composition has an effect on theinhibition of glowing to some extent, but shows no improvement inlow-temperature resistance.

JP-B-57-10898 discloses a resin composition obtained by incorporating acarbon powder such as carbon black, as a flame retardant aid, into aself-distinguishing thermoplastic resin composition containing magnesiumhydroxide. The disclosed resin composition shows some improvement inflame retardancy, but shows no improvement in low-temperatureresistance. Further, JP-B-57-10898 describes nothing concerning thelow-temperature resistance.

JP-A-60-243155 seeks to achieve excellent moldability and excellentappearance, physical properties and flame retardancy of a molded articleby incorporating a specific magnesium hydroxide into a thermoplasticresin. The specific magnesium hydroxide refers to a magnesium hydroxidehaving excellent dispersibility and non-aggregation properties andhaving a BET specific surface area of 20 m² /g or less and a BETspecific surface area/Blaine permeability method specific surface arearatio of 1˜3. However, JP-A-60-243155 does not at all mention thelow-temperature resistance, and no composition according toJP-A-60-243155 is satisfactory in low-temperature resistance.

As explained above, no prior art documents seek to improve thelow-temperature resistance, nor are the compositions according to theprior art documents are satisfactory in the improvement oflow-temperature resistance. For providing a flame-retardant polyolefinresin composition practically suited for use in a low-temperatureenvironment, it is required to accomplish all of low-temperatureresistance, surface whitening resistance, flame retardancy and anadequate melt index at the same time.

In the expansion-molding method, further, it is required to provide anexpansion-molded article having uniform and fine gas bubbles withoutlarge-sized gas bubbles. The large-sized gas bubbles decrease thestrength and heat insulation of the resin.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a halogen-freeflame-retardant polyolefin resin composition which can give a moldedarticle improved in low-temperature resistance, and a molded articleformed therefrom.

It is another object of the present invention to provide a halogen-freeflame-retardant polyolefin resin composition which can give a moldedarticle improved in low-temperature resistance and surface whiteningresistance and improved in flame retardancy and melt index.

It is further another object of the present invention to provide anexpansion-molded article having uniform and fine gas bubbles withoutlarge-sized gas bubbles by an expansion-molding method.

According to the present invention, the above objects and advantages ofthe present invention are achieved by a low-temperature-resistanthalogen-free flame-retardant polyolefin-based resin compositioncontaining

(a) 100 parts by weight of a polyolefin resin,

(b) 15 to 250 parts by weight of a dihydric or trihydric metal hydroxidesurface-treated with a saturated fatty acid having 10 to 30 carbon atomsor an alkali metal salt thereof, or, when the metal hydroxide isaluminum hydroxide, 15 to 250 parts by weight of aluminum hydroxidesurface-treated with a saturated or unsaturated fatty acid having 10 to30 carbon atoms or an alkali metal salt thereof, and

(c) 0.1 to 10 parts by weight of an aluminum salt of an unsaturatedfatty acid having 10 to 30 carbon atoms.

Further, according to the present invention, there is provided a moldedarticle formed from the above flame-retardant polyolefin-based resincomposition.

DETAILED DESCRIPTION OF THE INVENTION

The present inventor has found that the poor low-temperature resistanceof conventional halogen-free flame-retardant polyolefin-based resincompositions can be overcome to a great extent by incorporating adihydric or trihydric metal hydroxide surface-treated with a specificfatty acid or its alkali metal salt and an aluminum salt of a specificunsaturated fatty acid into a halogen-free polyolefin resin, so that theso-obtained polyolefin-based resin composition is improved in flameretardancy and melt index, a molded article formed from the so-obtainedpolyolefin-based resin composition is almost free of a surface whiteningphenomenon and that the above composition gives an excellentexpansion-molded article by an expansion molding method. Based on thesefinding, the present invention has been completed.

The halogen-free polyolefin resin used in the present invention includesolefin homopolymers such as polypropylene, high-density polyethylene,low-density polyethylene, ultralow-density polyethylene, linearlow-density polyethylene, polybutene-1 and poly-4-methylpentene-1; andolefin copolymers including copolymers composed of ethylene and othermonomer such as an ethylene-propylene copolymer, an ethylene-vinylacetate copolymer, an ethylene-ethyl acrylate copolymer, anethylene-butene-1 copolymer and an ethylene-propylene diene terpolymer.These resins may be used alone or in combination.

The metal hydroxide used in the present invention is a dihydric ortrihydric metal hydroxide and includes magnesium hydroxide, aluminumhydroxide, calcium hydroxide and calcium aluminate hydrate. Further, thedihydric or trihydric metal hydroxide may be a composite metal hydroxidewhich is a solid solution in which at least one of nickel, cobalt,manganese, iron, copper and zinc is dissolved in any one of the abovemetal hydroxides. The dihydric or trihydric metal hydroxide may be anyone of natural and synthetic products.

The average secondary particle diameter of the metal hydroxide used inthe present invention is preferably in the range of from 0.1 to 10 μm,more preferably 0.3 to 6 μm. When the average secondary particlediameter is within the above range, the flame-retardant polyolefin-basedresin composition has excellent mechanical strength and a molded articletherefrom has an excellent appearance. When the average secondaryparticle diameter of the metal hydroxide is outside the above range,undesirably, the above properties are poor and the resin composition ispoor in processability.

When the metal hydroxide other than aluminum hydroxide is used, themetal hydroxide is surface-treated with a saturated fatty acid having 10to 30 carbon atoms or an alkali metal salt thereof. When aluminumhydroxide is used, no surface whitening phenomenon is involved, and thealuminum hydroxide may be surface-treated with any one of the abovesaturated fatty acid and an unsaturated fatty acid having 10 to 30carbon atoms. This surface treatment of the metal hydroxide enhances thecompatibility between the metal hydroxide and the polyolefin resin,improves the processability of the resin composition, inhibits thesurface whitening phenomenon and improves the low-temperatureresistance.

The amount of the fatty acid or its alkali metal salt for the abovesurface treatment, per 100 parts by weight of the metal hydroxide, ispreferably 0.1 to 10 parts by weight, more preferably 0.2 to 5 parts byweight. When the metal hydroxide is surface-treated with an alkali metalsalt, and when the metal hydroxide is other than aluminum hydroxide, itis preferred in view of the inhibition of a surface whitening phenomenonto sufficiently wash the surface-treated metal hydroxide with water orwarm water such that the amount of the alkali metal remaining in theresultant surface-treated metal hydroxide is preferably not more than800 ppm, more preferably not more than 400 ppm.

The term "surface whitening phenomenon" in the present invention refersto the following phenomenon. When a molded article of a flame-retardantpolyolefin-based resin composition containing, for example, magnesiumhydroxide is placed in an atmosphere of air having a high humidity,magnesium hydroxide reacts with carbonic acid formed from water andcarbon dioxide gas to form magnesium carbonate and leaves a dent(concave portion) having a magnesium hydroxide particle size in themolded article surface by its elution. This in turn, causes visual lightto be scattered and the molded article surface to look white. Anothercause is that crystal of magnesium carbonate is deposited on the moldedarticle surface and the molded article surface looks white. Whenaluminum hydroxide which does not react with a weak acid such ascarbonic acid is used, this phenomenon does not take place.

The surface whitening phenomenon greatly hampers the surface appearanceof a molded article and degrades the product value of the moldedarticle. The inhibition of the surface whitening phenomenon has been aserious problem of a molded article obtained from a flame-retardantpolyolefin-based resin composition containing a metal hydroxide andmagnesium hydroxide in particular.

The surface treating agent used in the present invention is a saturatedor unsaturated fatty acid having 10 to 30 carbon atoms or an alkalimetal salt thereof. The saturated fatty acid includes stearic acid,behenic acid, capric acid, undecanoic acid, lauric acid, myristic acid,arachic acid, lignoceric acid, cerotic acid, montanic acid andmelissicacid. The unsaturated fatty acid include soleic acid, erucicacid, obtusilic acid, caproleic acid, undecylenic acid, linderic acid,tsuzuic acid, physeteric acid, myristoleic acid, palmitoleic acid,petroselinic acid, elaidic acid, cis-II-octadecenoic acid, vaccenicacid, gadoleic acid, cis-II-eicosenoic acid, cetoleic acid, brassidicacid, selacholeic acid, ximenic acid, lumequeic acid, linoleic acid andlinolenic acid. The alkali metal includes lithium,potassium and sodium.

The amount of the metal hydroxide surface-treated with the above surfacetreating agent, per 100 parts by weight of the polyolefin resin, is inthe range of 15 to 250 parts by weight. When the amount of the abovesurface-treated metal hydroxide is less than the above lower limit, theflame retardancy is insufficient. When the above amount is greater thanthe above upper limit, the polyolefin based resin composition showspractically insufficient mechanical strength.

The flame retardant aid suitable for use in the present inventionincludes carbon powders such as carbon black, activated carbon andgraphite; phosphorus-containing compounds such as red phosphorus,ammonium polyphosphate, triphenyl phosphate, trixylyl phosphate andxylenyl diphenyl phosphate; transition metal compounds such as nickeloxide, cobalt oxide, manganese oxide, iron oxide, copper oxide, zincoxide, zirconium oxide, vanadium oxide, Titan Yellow pigment, zirconiumsilicate, molybdenum oxide, zinc molybdate, zinc stannate and tin oxide;and organic fibers which are carbonized at a high temperature such as anacrylic fiber and a novoloid fiber. The flame retardant aid may besurface-treated as required.

The amount of the above flame retardant aid, per 100 parts by weight ofthe polyolefin resin, is in the range of 0 to 30 parts by weight. Whenthe amount of the flame retardant aid is greater than 30 parts byweight, the mechanical strength of the polyolefin-based resincomposition is decreased to a practically inadequate level, and such anamount is uneconomical.

In the aluminum salt of an unsaturated fatty acid used in the presentinvention, the unsaturated fatty acid preferably has 10 to 30 carbonatoms. The unsaturated fatty acid includes oleic acid, erucic acid,obtssilic acid, , caproleic acid, undecylenic acid, linderic acid,tsuzuic acid, physeteric acid, myristoleic acid, palmitoleic acid,petroselinic acid, elaidic acid, cis-II-octadecenoic acid, vaccenicacid, gadoleic acid, cis-II-eicosenoic acid, cetoleic acid, brassidicacid, selacholeic acid, ximenic acid, lumequeic acid, linoleic acid andlinolenic acid. The aluminum salt of an unsaturated fatty acid used inthe present invention includes mono-, di- and tri-aluminum salts ofunsaturated fatty acids. The sealuminum salts maybe used alone or incombination. The aluminum salt of an unsaturated fatty acid can beselected from those synthesized by known synthesis methods such as areaction between an aqueous solution of an unsaturated fatty acid metalsalt and aluminum inorganic acid salt and a reaction between aluminumalkoxide and an unsaturated fatty acid in a non-aqueous solvent. Thenon-aqueous solvent includes ethanol and benzene.

The aluminum salt of an unsaturated fatty acid is a rubbery and massivesubstance, and is difficult to process with a processing machine such asa resin extruder without any modification. It is therefore preferred tomix the aluminum salt of an unsaturated fatty acid with the metalhydroxide or the flame retardant aid used in the present invention witha mixer or a kneader for powders and knead them to form a powder orparticles.

The amount of the aluminum salt of an unsaturated fatty acid, per 100parts by weight of the polyolefin resin, is preferably 0.1 to 10 partsby weight, more preferably 0.5 to 10 parts by weight. When the amount ofthe aluminum salt of an unsaturated fatty acid is smaller than the abovelower limit, the effect on the improvement of low-temperature resistanceis insufficient. When the above amount is greater than the above upperlimit, a gummy substance is liable to adhere to the top of a die whenthe halogen-free flame-retardant polyolefin-based resin composition ofthe present invention is produced with a processing machine such as anextruder.

The main function/effect of the aluminum salt of an unsaturated fattyacid is to improve the low-temperature resistance, and further, thealuminum salt of an unsaturated fatty acid has a function and an effectas an improver of flame retardancy (flame retardant aid) and alubricant.

The method of mixing the polyolefin resin, the metal hydroxide, theflame retardant aid and the aluminum salt of an unsaturated fatty acidis not specially limited, and any means can be employed if thesecomponents can be homogeneously mixed. For example, there can beemployed a method in which the above components and other additive(s)are mixed in advance and the mixture is melt-kneaded with an open roll,a single-screw or twin-screw extruder or a Banbury mixer. The method ofmolding the so-obtained composition is not specially limited, either.For example, the composition can be molded by any one of an injectionmolding method, an extrusion method, a blow molding method, a pressforming method, a rotary molding method, a calender forming method and asheet forming method.

The flame-retardant polyolefin-based resin composition of the presentinvention may contain a variety of additives, reinforcement materialsand fillers which are generally used. Examples of these additives,reinforcement materials and fillers include an antioxidant, anultraviolet absorbent, a photostabilizer, a metal deactivating agent, acrosslinking agent, a colorant, a curing agent, a nucleating agent, afoaming agent, a deodorant, lithopone, clay, a wood powder, a glassfiber, ferrite, talc, mica, wollastonite, calcium carbonate, fibrousmagnesium hydroxide, fibrous basic magnesium sulfate, a metal fiber anda metal powder.

The present invention will be explained with reference to Exampleshereinafter, in which "part" and "%" stand for "part by weight" and "%by weight" unless otherwise specified. Methods of measurements of anaverage secondary particle diameter, low-temperature resistance, meltindex, flame retardancy, surface whitening phenomenon, BET specificsurface area, Blaine permeability method specific surface area andexpandability of expansion-molded article in Examples are as follows.

<Average Secondary Particle Diameter>

Magnesium hydroxide and aluminum hydroxide were measured with amicrotrack supplied by Leeds & Northrup Instruments Company.

<Low-Temperature Resistance>

Test pieces from a composition containing polypropylene and test piecesfrom a composition containing high-density polyethylene were allowed tostand at -20° C. for 48 hours and then measured for a du Pont impactstrength and an Izod impact strength according to JIS K7110. In the duPont impact strength measurement, the test pieces had the form of a diskhaving a diameter of 50 mm and a thickness of 2.1 mm, and an energyvalue when half of the test pieces cracked was taken as a du Pont impactvalue.

Test pieces from a composition containing an ultralow densitypolyethylene and test pieces from a composition containing anethylene-vinyl acetate copolymer (to be referred to as "EVA"hereinafter) were measured for a brittle temperature at a lowtemperature by the brittle temperature test according to JIS K7216.

<Melt Index>

Measured according to JIS K7210. Test pieces from a compositioncontaining polypropylene and test pieces from a composition containinghigh-density polyethylene were measured at 230° C. under a load of 2.16kg. Test pieces from a composition containing an ultralow-densitypolyethylene were measured at 190° C. under a load of 2.16 kg. Testpieces from a composition containing EVA were measured at 125° C. undera load of 2.16 kg.

<Flame Retardancy>

Test pieces having a thickness of 1/8inch or 1/12inch were measuredaccording to the UL94VE method.

<Surface Whitening Phenomenon>

A test piece having a thickness of 1/8inch, the same as the test pieceprepared for the test according to the UL94VE method, was completelyimmersed in 500 ml of ion-exchanged water and kept in the water at 24°C. for 48 hours with introducing carbon dioxide gas into the water.Thereafter, the degree of surface whitening was visually evaluated onthe basis of the following ratings.

Class 1: No surface whitening phenomenon

Class 2: Almost no surface whitening phenomenon is observed.

Class 3: A surface whitening phenomenon is observed only slightly.

Class 4: A surface whitening phenomenon is observed to some extent.

Class 5: A surface whitening phenomenon is observed on several parts onthe surface.

Class 6: A surface whitening phenomenon is observed on many parts on thesurface.

Class 7: A surface whitening phenomenon is observed on a large area.

Class 8: A surface whitening phenomenon is observed all over thesurface.

A test piece coming under class 4 to class 1 means that the test piecehas the practical capability of preventing the surface whiteningphenomenon, and a test piece coming under class 3 to class 1 isparticularly preferred.

<BET Specific Surface Area>

Measured according to the method described in "Catalyst" (Vol. 2, No.4,473, 1960, written by Tokuji Takagi).

<Blaine Permeability Method Specific Surface area>

A sample was measured according to JIS R5201-1964 on an assumption thatthe sample had a porosity of 0.714.

<Expandability of Expansion-Molded Article>

An expansion-molded article was cut or fractured (bronken), and gasbubbles were measured for sizes while the cut or fractured surfacewereobserved through a precision ruler, a magnifying glass or an opticalmicroscope.

EXAMPLES 1˜5 AND COMPARATIVE EXAMPLES 1˜14

                                      TABLE 1                                     __________________________________________________________________________    Poly-   Mg hydroxide          Improver for                                    propy-  Surface-    Flame     low                                             lene,   treated     retardant temperature                                     Amount  with   Amount                                                                             aid   Amount                                                                            resistance                                                                          Amount                                    __________________________________________________________________________    Ex.1                                                                              100 Na stearate                                                                          130  No    --  Al oleate                                                                           3                                         CEx.1                                                                             100 "      130  No    --  No    --                                        CEx.2                                                                             100 "      150  No    --  No    --                                        CEx.3                                                                             100 No     130  No    --  No    --                                        CEx.4                                                                             100 No     150  No    --  No    --                                        CEx.5                                                                             100 No     130  No    --  Mg stearate                                                                         3                                         CEx.6                                                                             100 No     130  Na stearate                                                                         7   Al distearate                                                                       7                                         CEx.7                                                                             100 No     130  No    --  Al oleate                                                                           3                                         CEx.8                                                                             100 Na Oleate                                                                            130  No    --  "     3                                         CEx.9                                                                             100 Na stearate                                                                          130  EVA   3   No    --                                        CEx.10                                                                            100 No Mg  0    No    --  No    --                                        Ex.2                                                                              100 Na stearate                                                                          110  Carbon black                                                                        3   Al oleate                                                                           3                                         CEx.11                                                                            100 "      110  "     3   No    --                                        Ex.3                                                                              100 "      30   A,B,C     Al oleate                                                                           3                                         Ex.4                                                                              100 "      45   A,B,C     "     5                                         Ex.5                                                                              100 "      50   A,B,C     "     1                                         CEx.12                                                                            100 "      30   A,B,C     No    --                                        CEx.13                                                                            100 "      45   A,B,C     No    --                                        CEx.14                                                                            100 "      50   A,B,C     No    --                                        __________________________________________________________________________     Notes: Ex. = Example, CEx. = Comparative Example, A = 10 parts by weight      of red phosphorus, B = 5 parts by weight of carbon black, C = 1 parts by      weight of acrylic fiber                                                  

Components shown in Table 1 in amounts shown in Table 1, 0.25 part, per100 parts of the polypropylene, of "DLTP" (supplied by YoshitomiPharmaceutical Co., ltd.) as an antioxidant and 0.25 part, per 100 partof the polypropylene, of "Irganox 1010" (supplied by Ciba Geigy AG) asan antioxidant were mixed in advance, and the mixture was melt-kneadedat 230° C. with a single-screw extruder to prepare pellets having a sizeof about 3 mm. Part of pellets were measured for a melt index, and theremaining pellets were injection-molded to prepare test pieces.

The polypropylene used in all of Examples 1˜5 and Comparative Examples1˜14 was an impact-resistance grade product. The magnesium hydroxide wasa synthetic product having a BET specific surface area of 8 m² /g, a BETspecific surface area/Blaine permeability method specific surface arearatio of 1.5 and an average secondary particle diameter of 0.7 μm. Thismagnesium hydroxide was prepared according to the method disclosed inJP-A-60-243155.

Comparative Examples 3˜7 used the magnesium hydroxide which was notsurface-treated.

Examples 1˜5 and Comparative Examples 1, 2, 9 and 11˜14 used themagnesium hydroxide surface-treated with 3 parts by weight, per 100parts by weight of the magnesium hydroxide, of sodium stearate.

Comparative Example 8 used the magnesium hydroxide surface-treated with2 parts by weight, per 100 parts by weight of the magnesium hydroxide,of sodium oleate.

In Examples 3˜5 and Comparative Examples 12˜14, the red phosphorus was"Novaexcel 140" supplied Rin Kagaku Kogyo K. K., the carbon black wasFEF (fast extruding furnes), and the acrylic fiber was a copolymer whichwas formed from acrylonitrile and vinyl acetate and was in a 1.5 denierchopped strand state.

The carbon black used in Example 2 and Comparative Example 11 was thesame as the above FEF.

The aluminum oleate used in Examples 1˜5 and Comparative Examples 7 and8 was obtained by a reaction between a sodium oleate aqueous solutionand an aluminum chloride hexahydrate aqueous solution.

Comparative Example 5 used, as magnesium stearate, a reagent supplied byWako Purechemical Industries, Ltd.

Comparative Example 6 used, as aluminum distearate, a reagent suppliedby Wako Purechemical Industries, Ltd.

The EVA used in Comparative Example 9 had a vinyl acetate content of20%.

The sodium stearate and the sodium oleate used as a surface treatingagent were reagents for chemistry supplied by Wako PurechemcialIndustries, Ltd.

Table 2 shows the test results.

                  TABLE 2                                                         ______________________________________                                        Low temperature                                                                             Surface          Flame                                          resistance    whitening                                                                              Melt    retardancy                                     Izd       du Pont resis-   Index UL94VE                                       impact    impact  tance    g/10  Thick-                                                                              Evalua-                                value     value   Class    minutes                                                                             ness  tion                                   ______________________________________                                        Ex.1  4.0     50      3      6.8   1/8   V-0                                  CEx.1 1.9     10      3      4.0   1/8   non-                                                                          standardized                         CEx.2 1.4     5       3      3.7   1/8   V-0                                  CEx.3 1.2     ≦5                                                                             8      0.15  1/8   non-                                                                          standardized                         CEx.4 0.8     ≦5                                                                             8      0.11  1/8   V-0                                  CEx.5 1.5     10      3      3.6   1/8   non-                                                                          standardized                         CEx.6 1.9     ≦5                                                                             8      6.2   1/8   non-                                                                          standardized                         CEx.7 1.8     5       8      3.6   1/8   non-                                                                          standardized                         CEx.8 4.2     55      8      6.4   1/8   V-0                                  CEx.9 1.7     10      3      4.0   1/8   non-                                                                          standardized                         CEx.10                                                                              4.1     15      1      2.0   1/8   non-                                                                          standardized                         Ex.2  5.6     50      3      5.1   1/8   V-1                                  CEx.11                                                                              2.0     10      3      2.9   1/8   non-                                                                          standardized                         Ex.3  3.1     25      2      3.4   1/8   V-0                                  Ex.4  3.5     30      2      3.6   1/12  V-0                                  Ex.5  3.0     25      2      3.1   1/12  V-0                                  CEx.12                                                                              1.8     ≦5                                                                             2      2.3   1/8   non-                                                                          standardized                         CEx.13                                                                              1.9     ≦5                                                                             2      2.6   1/12  non-                                                                          standardized                         CEx.13                                                                              1.7     ≦5                                                                             2      2.1   1/12  non-                                                                          standardized                         ______________________________________                                         Notes to Table 2: Ex. = Example, CEx. = Comparative Example, Unit of Izod     impact value = kgf · cm/cm, Unit of du Pont impact value = kgf       · cm, Unit of thickness = inch                                  

Notes to Table 2: Ex. =Example, CEx. =Comparative Example, Unit of Izodimpact value =kgf.cm/cm, Unit of du Pont impact value =kgf.cm, Unit ofthickness =inch

The test results of Examples 1˜5 were excellent concerning all of thetests such as surface whitening phenomenon, flame retardancy,low-temperature resistance and melt index, while the test results ofComparative Examples 1˜14 were poor concerning at least one of the abovetests.

EXAMPLE 6 AND COMPARATIVE EXAMPLE 15

                                      TABLE 3                                     __________________________________________________________________________                  Metal hydroxide                                                               Magnesium                                                                     hydroxide    Improver for                                                     surface-     low-                                               Polyolefin    treated      temperature                                        resin     Amount                                                                            with    Amount                                                                             resistance                                                                          Amount                                       __________________________________________________________________________    Ex.6                                                                              High-density                                                                        92  Potassium                                                                             150  Al erucate                                                                          3                                                polyethylene                                                                            behenate                                                            EVA   8                                                                   CEx.15                                                                            High-density                                                                        92  Potassium                                                                             150  No    --                                               polyethylene                                                                            behenate                                                            EVA   8                                                                   __________________________________________________________________________     Ex. = Example, CEx. = Comparative Example                                

Components shown in Table 3 in amounts shown in Table 3 and 0.5 part,per 100 parts of the total of the high-density polyethylene (92 parts)and EVA (8 parts), of "Irganox 1010" as an antioxidant were mixed inadvance, and the mixture was melt-kneased at 230° C. with a twin-screwextruder to prepare pellets having a size of about 3 mm. Part of thepellets were measured for a melt index, and the remaining pellets wereextruded to prepare test pieces for various property tests except forthe du Pont impact test, test pieces for which were prepared bycompression molding. The high-density polyethylene was a product of anextrusion grade. EVA was a product having a vinyl acetate content of20%. The magnesium hydroxide was a natural product having a purity of91% and an average secondary particle diameter of 5.0 μm. The magnesiumhydroxide was surface-treated with 2 part by weight, per 100 parts byweight of the magnesium hydroxide, of potassium behenate before use.

The aluminum erucate was prepared by a reaction of aluminum, alkoxideand erucic acid in ethanol.

Table 4 shows the results.

                  TABLE 4                                                         ______________________________________                                        Low temperature                                                                             Surface          Flame                                          resistance    whitening                                                                              Melt    retardancy                                     Izd       du Pont resis-   Index UL94VE                                       impact    impact  tance    g/10  Thick-                                                                              Evalua-                                value     value   Class    minutes                                                                             ness  tion                                   ______________________________________                                        Ex.6  6.2     60      3      2.0   1/8   V-0                                  CEx.15                                                                              3.6     20      3      1.2   1/8   non-                                                                          standardized                         ______________________________________                                         Ex. = Example, CEx. = Comparative Example                                

As shown in Table 4, the result of the test for the low-temperatureresistance in Example 6 is greatly improved over that in ComparativeExample 15, and the results of the tests for flame retardancy and meltindex are also greatly improved over those in Comparative Example 15.Further, the molded article in Example 6 showed a surface whiteningphenomenon only slightly, and it is therefore seen that the compositionin Example 6 is practically suitable for use in a low-temperatureenvironment.

EXAMPLE 7 AND COMPARATIVE EXAMPLE 16

                                      TABLE 5                                     __________________________________________________________________________                    Metal hydroxide                                                               Aluminum     Improver for                                                     hydroxide surface-                                                                         low-temperature                                  Polyolefin resin                                                                          Amount                                                                            treated with                                                                           Amount                                                                            resistance                                                                            Amount                                   __________________________________________________________________________    Ex. 7                                                                             Ultralow-density                                                                      100 Sodium   130 Aluminum                                                                              3                                            polyethylene                                                                              oleate       oleate                                           CEx. 16                                                                           Ultralow-density                                                                      100 Sodium   130 No      --                                           polyethylene                                                                              oleate                                                        __________________________________________________________________________     Ex. = Example, CEx. = Comparative Example                                

Components shown in Table 5 in amounts shown in Table 5 and 0.5 part,per 100 parts of the ultralow-density polyethylene, of "Irganox 1010" asan antioxidant were mixed in advance, and the mixture was melt-kneasedat 190° C. with a single-screw extruder to prepare pellets having a sizeof about 3 mm. Part of the pellets were measured for a melt index, andthe remaining pellets were compression-molded to prepare test pieces forvarious property tests.

The ultralow-density polyethylene had a density of 0.90 and a melt indexof 0.40 g/10 minutes. The aluminum hydroxide was a synthetic producthaving an average secondary particle diameter of 1.15 μm. The aluminumhydroxide was surface-treated with 0.4 part by weight, per 100 parts byweight of the aluminum hydroxide, of sodium oleate before use. Thealuminum oleate was the same as that used in Example 1.

Table 6 shows the results.

                  TABLE 6                                                         ______________________________________                                                      Surface                                                         Low temperature                                                                             whitening                                                                              Melt    Flame retardancy                               resistance    resis-   Index   UL94VE                                         Brittle       tance    g/10    Thick-                                                                              Evalua-                                  temperature   Class    minutes ness  tion                                     ______________________________________                                        Ex. 7 -60° C. or lower                                                                   1        0.25  1/8   V-0                                    CEx. 16                                                                             -30° C.                                                                            1        0.02  1/8   non-                                                                          standardized                           ______________________________________                                         Ex. = Example, CEx. = Comparative Example                                

As shown in Table 6, the results of Example 7 are greatly improved overthe results of Comparative Example 16 not only in flame retardancy butalso in low-temperature resistance and melt index. The great improvementin melt index means that an ultralow-density polyethylene containingaluminum hydroxide, of which the processing with an extruder isimpossible or very difficult, is improved in processability to such alevel of melt index that it is easily processable.

EXAMPLE 8 AND COMPARATIVE EXAMPLE

                                      TABLE 7                                     __________________________________________________________________________                    Metal hydroxide                                                               Aluminum     Improver for                                                     hydroxide surface-                                                                         low-temperature                                  Polyolefin resin                                                                          Amount                                                                            treated with                                                                           Amount                                                                            resistance                                                                            Amount                                   __________________________________________________________________________    Ex. 8                                                                             EVA resin                                                                             100 Sodium   130 Aluminum                                                                              3                                                        palmitate    oleate                                           CEx. 17                                                                           EVA resin                                                                             100 Sodium   130 No      --                                                       palmitate                                                     __________________________________________________________________________     Ex. = Example, CEx. = Comparative Example                                

Components shown in Table 7 in amounts shown in Table 7, 1 part, per 100parts of the EVA resin, of "Irganox 1010" as an antioxidant and 0.5part, per 100 parts of the EVA resin, of "DCP" (dicumyl peroxide,supplied by Sumitomo Chemical Co., Ltd.) were mixed in advance, and themixture was melt-kneaded at 120° C. with a single-screw extruder toprepare pellets having a size of about 3 mm. Part of the pellets weremeasured for a melt index. The remaining pellets were pre-molded with apress-forming machine at 120° C. for 5 minutes and then crosslinked withthe press-forming machine at 180° C. for 15 minutes, and test pieces forvarious property tests were prepared from the crosslinked product.

EVA was a product having a vinyl acetate content of 25%. The magnesiumhydroxide was a synthetic product having an average secondary particlediameter of 0.48 μm. The magnesium hydroxide was surface-treated with 5parts by weight, per 100 parts by weight of the magnesium hydroxide, ofsodium palmitate before use Table 8 shows the results.

                  TABLE 8                                                         ______________________________________                                                      Surface                                                         Low temperature                                                                             whitening                                                                              Melt    Flame retardancy                               resistance    resis-   Index   UL94VE                                         Brittle       tance    g/10    Thick-                                                                              Evalua-                                  temperature   Class    minutes ness  tion                                     ______________________________________                                        Ex. 8 -60° C. or lower                                                                   3        1.1   1/8   V-0                                    CEx. 17                                                                             -40° C.                                                                            3        0.3   1/8   non-                                                                          standardized                           ______________________________________                                         Ex. = Example, CEx. = Comparative Example                                

As shown in Table 8, the use of EVA resin produces great improvement inall of flame retardancy, low-temperature resistance and melt index.

The resin compositions obtained in Examples 1 to 5 and ComparativeExamples 1 to 14 were evaluated for expandability of theirexpansion-molded article as follows.

Azodicarbonamide as an expanding agent was added to pellets of a resincomposition when the pellets were injection-molded, that is, the pelletswere injection expansion-molded. The azodicarbonamide was used in anamount of 1.5 parts by weight per 100 parts by weight of the resincomponent (polypropylene) of the resin composition. The above injectionexpansion molding was carried out at a temperature of 220° C., to obtainan expansion-molded article having a thickness of 1/4inch.

The above expansion-molded article was cut and fractured and gas bubblespresent in the fractured and cut surface were measured for sizes througha precision ruler, a magnifying glass or an optical microscope. In theexpansion-molded articles of the resin compositions obtained in Examples1 to 5 and Comparative Example 10, gas bubbles having a size of about200 μm or smaller were uniformly found around a central place of thethickness of each. In the expansion-molded articles of the resincompositions obtained in Comparative Examples 1 to 9 and 11 to 14, manygas bubbles having a size of about 1 mm or smaller were found around acentral place of the thickness of each, and gas bubbles having a size of200 μm or smaller were scarcely found.

The resin composition obtained in Comparative Example 10 contained noflame retardant, and gas bubbles having a size of about 200 μm orsmaller were uniformly found around the central place of the thickness.

According to the present invention, there is provided a halogen-freeflame-retardant polyolefin-based resin composition which is greatlyimproved in melt index and can give a molded article which is almostfree from a surface whitening phenomenon, improved in flame retardancyand greatly improved in low-temperature resistance. According to thepresent invention, there is provided a novel halogen-freeflame-retardant polyolefin-based resin composition which can give amolded article suitable for use in a low-temperature environment such asa cold district or an extremely cold district.

According to the present invention, there is provided anexpansion-molded article of a halogen-free flame-retardantpolyolefin-based resin composition, which molded article has uniform andfine gas bubbles without gas bubbles having a large size.

What is claimed is:
 1. A low-temperature-resistant halogen-freeflame-retardant polyolefin-based resin composition containing(a) 100parts by weight of a polyolefin resin, (b) 15 to 250 parts by weight ofa dihydric or trihydric metal hydroxide surface-treated with a saturatedfatty acid having 10 to 30 carbon atoms or an alkali metal salt thereof,or, when the metal hydroxide is aluminum hydroxide, 15 to 250 parts byweight of aluminum hydroxide surface-treated with a saturated orunsaturated fatty acid having 10 to 30 carbon atoms or an alkali metalsalt thereof, and (c) 0.5 to 10 parts by weight of an aluminum salt ofan unsaturated fatty acid having 10 to 30 carbon atoms.
 2. A compositionaccording to claim 1, wherein the metal hydroxide has an averagesecondary particle diameter of 0.1 to 10 μm.
 3. A composition accordingto claim 1, wherein the metal hydroxide is a product surface-treatedwith 0.1 to 10 parts by weight, per 100 parts by weight of the metalhydroxide, of a fatty acid or the alkali metal salt thereof.
 4. Acomposition according to claim 1, wherein the composition furthercontains not more than 30 parts by weight of a flame retardant aidselected from the group consisting of a carbon powder, aphosphorus-containing compound, a transition metal compound, an acrylicfiber and a novoloid fiber.
 5. A composition according to claim 1,wherein the dihydric or trihydric metal hydroxide is at least one memberselected from the group consisting of magnesium hydroxide, aluminumhydroxide, calcium hydroxide and calcium aluminum hydrate.
 6. Acomposition according to claim 5, wherein the dihydric or trihydricmetal hydroxide is a composite metal hydroxide in which a metal atomselected from the group consisting of nickel, cobalt, manganese, iron,copper and, Zinc is dissolved in the metal hydroxide recited in claim 5.